Imaging system

ABSTRACT

A developer material comprising colored toner particles having a particle size less than about 30 microns and a minor proportion of submicroscopic silicon dioxide additive particles having at least a portion of the silicon atoms on the outside surface of the silicon dioxide particles directly attached through an oxygen atom to another silicon atom which is in turn directly attached through a carbon linkage to one to three organic groups.

United, States Patent Chatterji et al. a t

[451 June 25, 1974 IMAGING SYSTEM Inventors: Arun K. Chatterji; Marianne1 Custazzo; Demosthemes K.

Kiriazides, all of Webster, N.Y.; John J. Russell, Jr., Tyrone, Pa.;John P.-Serio, Webster, NY.

Assignee:

Xerox Corporation, Stamford, Conn. by said John J. Russell, Jr.

Filed: Sept. 25, 1972 App]. No.: 292,234

Related U.S. Application Data Division of Ser. No. 39,856, May 20, i970.

U.S. Cl. 96/1 SD, 252/62.l Int.- Cl ..-G03g 13/08 Field of Search 96/1,1 SP1 252/62.l P

References Cited UNITED STATES PATENTS 5/l96l Wielicki 252/62.l

6/1962 Wielicki ..252/62.l 9/1972 Merrill... ..252/62.l

Primary Examiner-Ronald H. Smith Assistant Examiner-John L. Goodrow [57]ABSTRACT 2 Claims, No Drawings IMAGING SYSTEM May 20, 1970. t

' BACKGROUND OF THE INVENTION This invention relates to imaging systems,and more particularly, to improvedelectrostatographic developingmaterials, their manufacture and use.

The formation and development of imagesv on the surface ofphotoconductor materials by electrostatic means is well known. The basicxerographic process, as taught by C. F. Carlson in US. Pat. No.2,297,691, involves placing a uniformelectrostatic charge on aphotoconductive insulating layer, exposing the layer to alight-and-shadow image to dissipate the charge on the areas of the layerexposed to the light and developing the resulting electrostatic latentimage by depositing on the image a finely divided electroscopic materialreferred toin the art as toner. The toner will normally be attracted tothose areas of the layer which retain a charge, thereby forming a tonerimage corresponding to the electrostatic latent image. This powder imagemay then be transferred to a support surface such as paper. Thetransferred image may be subsequently be permanently affixed to thesupport surface as by heat. Instead of latent image formation byuniformly charging the photoconductive layer and then exposing the layerto a light-and-shadow image, one may form the latent image by directlycharging the layer in image configuration. The powder image may be fixedto the photoconductive layer of elimination of the powder image transferstep is desiredJOther suitable fixing means such as solvent orovercoating treatment may be substituted for the foregoing heat fixingsteps.

Several methods are known for applying the electroscopic particles tothe electrostatic latent image to be developed. One development method,as disclosed by E. N.-Wise in US. Pat. No. 2,618,552 is known ascascade" development. In this method, a developer materialcomprisingrelatively large carrier particles having finely-divided tonerparticles electrostatically coated thereon is conveyed to and rolled orcascaded across the electrostatic latent image bearing surface. Thecomposition of the carrier particles is so selected as totriboelectrically charge the toner particles to the desired polarity. Asthe mixture cascades or rolls across the image bearing surface, thetoner particles are electrostatically deposited and secured to thecharged portion of the latent imageand are not, deposited on theuncharged or background portions of the image. Most of the tonerparticles accidently. deposited in the background are removed by therolling carrier, due'apparently, to the greater electrostatic attractionbetween the toner and the carrier than between the toner and thedischarged background. The carrier and excess surface and thetoner'particles are drawn from the brush to the latent image byelectrostatic attraction.

Still another technique for developing electrostatic latent images isthe powder cloud process as disclosed, for example, by C. F. Carlson inU.S. Pat. No. 2,221,776. In this method, a developer material comprisingelectrically charged toner particles in a gaseous fluid is passedadjacent the surface bearing the electrostatic latent image. The tonerparticles are drawn by electrostatic attraction from the gas to thelatent image. This process is particularly useful in continuous tonedevelopment.

Other development methods such as touchdown development as disclosed byR. W. Gundlach in US. Pat. No. 3,166,432 may be used where suitable.

Although some of the foregoing development techniques are employedcommercially today, the most widely used commercial electrostatographicdevelopment technique is the technique known as cascade development. Ageneral purpose office copying machine incorporating this developmentprocess is described in US. Pat. No. 3,301,126. In automaticelectrostatographic imaging equipment, it is conventional to employ anelectrophotographic plate in the form of a cylindrical drum which iscontinuously rotated through a cycle of sequential operations includingcharging, exposing, developing, transferring and cleaning. The plate isusually charged with corona of positive polarity by means of a coronagenerating device of the type disclosed by L. E. Walkup in US. Pat. No.2,777,957 which is connected to a suitable source of high potential.After forming a powder image on the electrostatic latent image duringthe development step, the powder image is'electrostatically transferredto a support surface by means of a corona generating device such as thecorona device mentioned above. In automatic equipment employing arotating drum, a support surface to which a powder image is to betransferred is moved through the equipment at the same rate as theperiphery'of the drum and contacts the drum at the transfer positioninterposed between the drum surface and the corona generating device.Transfer is effected by a corona generating-device which imparts anelectrostatic charge to attract the powder image from the drum to thesupport surface. The polarity of charge required to effect imagetransfer is dependent upon the visual form of the original copy relativeto the reproduction and the electroscopic characteristics of thedeveloping material employed to effect development. For example, where apositive reproduction is to be made of the positive original, it isconventional to employ a positive polarity corona to effect transfer ofa negatively charged toner image to a support surface. When a positivereproduction from a negative original is desired, it is conventional toemploy a positively charged developing material which is repelled by thecharge areas on the plate to the discharged area thereon to form apositive image which may be transferred by negative polarity corona.This imaging process is ordinarily repeated for each copy produced bythe machine thousands of times during the usuable life of the developerand drum surface.

Although automatic electrostatographic imaging machines are describedabove with reference to cascade development systems, it is apparent thatother well known development techniques such as those described abovewould also utilize cycles of sequential operations including charging,exposure and developing. Generally, thousands of cycles of service freeperformance is expected of automatic machines today. Thus, the developeremployed in automatic electrostatographic imaging machines must bedurable and exhibit stable and predictable performance for extendedperiods of time.

Many developer materials, though initially possessing desirableproperties such as proper triboelectric characteristics, are unsuitablebecause they tend to exhibit a change in performance characteristicsover extended periods of time. The change in performance characteristicsis a result of numerous factors. For example, the electrical propertiesof some toner and carrier materials fluctuate with changes in relativehumidity and are not desirable for employment in electrostatographicimaging systems, particularly in precision high speed automatic machineswhich require toners and carriers having stable and predictabletriboelectric values. Another factor affecting predictability ofdeveloper performance in automatic machines is the formation ofcontaminating films of toner material on reusable photoreceptor imagingsurfaces and carrier particle surfaces. When toner and carrier particlesare employed in automatic machines and recycled through many thousandsof cycles, the millions of collisions which occur between the tonerparticles, carrier particles and other surfaces in the machine causedthe toner particles to be welded or otherwise forced onto the surfacesof photoreceptors and carrier particles. It is apparent that the gradualaccumulation of permanently attached toner material on the surfaces ofcarrier particles causes a change in the triboelectric value of thecarrier particles and directly contributes to the degradation of thecopy quality by eventual destruction of the toner carrying capacity ofthe carrier. Similarly, gradual accumulation of unwanted toner films onthe surface of reusable photoreceptors alters the electrical propertiesof the photoreceptor thereby altering the overall performances of theautomatic electrostatographic imaging machine. Developer deteriorationin automatic electrostatographic imaging machines isvisually detected onimaged copies in the form of increased toner deposits in the backgroundareas, poor image resolution and low image density in solid areas. Thus,there is a continuing need for a better system for forming toner imagesin the electrostatographic imaging machines.

SUMMARY OF THE INVENTION It is, therefore an object of this invention toprovide an imaging system which overcomes the above-noted deficiencies.y

it is another object of this invention to provide an imaging systemwhich stabilizes developer performance.

It is another object of this invention to provide an imaging systemwhich forms images having reduced toner deposits in background areas.

It is another object of this invention to provide an imaging systemwhich provides images having dense solid areas.

it is another object of this invention to provide an imaging systemwhich forms higher resolution images.

It is another object of this invention to provide an imaging systemwhich reduces the formation of toner films on carrier particle surfaces.

it is another object of this invention to provide an imaging systemwhich reduces toner film formation on photoreceptor surfaces.

It is another object of this invention to provide developing materialshaving physical and chemical properties superior to those of knowndeveloping materials.

The above objects and others are accomplished, generally speaking, byproviding a developer material comprising colored toner particles havinga particle size less than about 30 microns and a minor proportion ofsubmicroscopic silicon dioxide additive particles having at least aportion of the silicon atoms on the outside surface of the silicondioxide particles directly attached through a silicon to carbon linkageto one to three organic groups The additive particles may be introducedinto the ultimate developer material in any suitable manner to form aphysical mix of additive particles with developing material particles.Thus, for example, the additive particles may be initially mixed withcarrier particles or toner particles and thereafter introduced into thedeveloper mix. Generally, when the additive is physically mixed withtoner or carrier particles, satisfactory results are achieved when about.01 to about 15 percent additive based on the weight of the tonerparticles is employed. Greater stability of performance is achieved whenthe additive is present in an amount, from about .05 percent to about1.5 percent based on the weight of the toner in the final developermixture. For optimum stability of performanance for prolonged periods ofoperating time, about 0.25 to about 1 percent additive based on theweight of the toner should be employed.

Any suitable submicron particulate silicon dioxide additive having atleast a portion of the silicon atoms on the outside surface of theadditive particles directly attached to one to three hydrocarbon orsubstituted bydrocarbon groups may be employed in the developer of thisinvention. The silicon dioxide particles may be produced by any suitabletechnique such as the aqueous sodium silicate solution precipitation andsilica tetrachloride high temperature oxidation processes. One wellknownhigh temperature technique for forming the silicon dioxide particlesincludes flame hydrolysis decomposition of pure silicon tetrachloride inthe gaseous phase in an oxyhydrogen flame at about l,l00C. Satisfactoryresults are obtained with treated silicon dioxide particles in a rangeof about 1 millimicron to about millimicrons. Optimum stability underhigh humidity conditions and extended periods of use are achieved withparticles having a size between about 2 and about 50 millimicrons. Theadditives of this invention may be of any suitable shape. Typical shapesinclude spherical, granular and irregular particles. Optimum results areobtained with additive particles having a spherical shape because moreuniform developer flow properties are achieved. Although reference hasbeen made to substantially pure silicon dioxide particles, it isapparent that other material may be present in minor amounts. Forexample, if desired, a mixture of silicon dioxide and aluminum oxide maybe formed by mutual flame hydrolysis of silicon tetrachloroide andaluminum chloride. Analysis by x-ray indicates that the silicon dioxideparticles formed by flame hydrolysis are amorphous.

Prior to reaction with the organosilicon compounds, the submicroscopicsilicon dioxide particles employed in the developers of this inventionhave numerous silanol groups available for reaction on the particlesurfaces. For example, submicroscopic silicon dioxide particles having adiameter between about and about 40.millimicron s formed by falmehydrolysis have about one silanol group per about 28 to about 33A Thisamounts to about 2,000 silanol groups per silicon dioxide particle. Uponexposure of freshly prepared submicroscopic silicon dioxideparticles tothe ambient atmosphere, chemisorbed water molecules become attached tothe silanol groups. The presence of water molecules causes a chemicalreaction to occur between the water molecules and the organosiliconcompounds rather than between the silanol groups and the organo siliconcompounds. Thus, the sooner freshly prepared colloidal silica particlesare reacted with the organo silicon compounds, the greater number'ofsilanol groups will be available for reaction with the organo siliconcompound. The chemical attachment of hydrocarbon or substitutedhydrocarbon groups to at least a portion of the silicon atoms on thesurface of the silicon dioxide particles may be accomplished by anysuitable technique. In one technique, silicon dioxide particles freshlyobtained by the flame hydrolysis process described above is separated ina cyclone separator from the bulk of the hydrochloric acid also formedduring the process. The silicon dioxide particles; at least oneorganosilicon compound having hydrocarbon or substituted hydrocarbongroups as well as hydrolyzable groups attached to .a silicon atom suchas dimethyl dichlorosilane; and steam are pneumatically introduced inparallel flow into a fluidized bed reactor heated to about 400C by meansof an inert gas such as nitrogen. The organosilicon compound reacts withsilanol groups on the surface of the silicon dioxide particles andchemical attachment between the silicon atom in the organosiliconcompound and a silicon atom in the silicon dioxide particle occursthrough an oxygen atom. Where theorganosilicon compounds have more thanone hydrolyzable group attached to each silicon atom in theorganosilicon compound, there is a possibility that (l) the silicon atomin the organosilicon compound may be chemically attached to two siliconatoms in the silicon particle through silicon-oxygen-silicon bonding;(2) the silicon atom in the organosilicon compound may be bonded to asilicon atom in the silicon dioxide particle and to a silicon atom inanother organosilicon compound through silicon-oxygen-silicon bonding;or (3) the silicon atom in the organosilicon compound may be attached toa silicon atom in the dioxide particle through a silicon-oxygen-siliconbond and the remaining hydrolyzable groups may be hydrolyzed leavinghydroxyl groups attached to the silicon atom of the organosiliconcompound. Where an organosilicon compound having two hydrolyzable groupssuch as dimethyl dichlorosilane is employed, it is believed that thesilicon atoms in two adjacent organosilicon compound molecules areattached through siliconoxygen-silicon bonding to each other as well asto silicon atoms in a silicon dioxide particle. This belief is supportedby measurements of hydroxyl group density before and after reaction andby the hydrophobic properties exhibited by the silicon dioxide particlesafter treatment. In any event, at least one hydrophobic hydrocarbon orsubstituted hydrocarbon group is'chemically attached bysilicon-oxygen-silicon bonding to a silicon atom in the silicon dioxideparticle. Obviously,

some developer stability improvement occurs when at least some of thesilanol groups available on the colloidal silica particles are reactedwith the silane. For a noticeable improvement in stability, at leastabout 5 percent of the silanol groups on the surfaces of the silicondioxide particles should be reacted with the organosilicon compounds. Atleast about 50 percent of the silanol groups should be reacted withorganosilicon compound for significantly improved developer stabilityunder high humidity conditions. Optimum results are achieved when atleast about percent of the silanol groups are reacted with theorganosilicon compounds. The foregoing percentages are based on anaverage surface silanol group density of about 3 silanol groups per 100Aof silicon dioxide particle surface area. Freshly prepared silicondioxide particles fonned by the flame hydrolysis technique describedabove have about 3 silanol groups per 100A of surface. The surfacesilanol group density on the surface of submicroscopic silicon dioxideparticles formed by any of the techniques described above may beregulated by heat treatment in vacuo. The heat treatment removeschemisorbed water and depending on the temperature employed, alsoremoves some of the hydroxyl groups. Thus, at equilibrium in a heattreatment in vacuo, the number of silanol groups per unit area ofsurface is about 5 silanol groups per 100A of surface at 150C and about1 silanol group per 100A of surface at 800C.

The marked difference in characteristics between ordinary-silicondioxide particles and silicon dioxide particles in which silanol groupshave been reacted with organosilicon compounds may be illustrated byplacing the reacted and unreacted particles in a beaker of wa- .ter.When unreacted submicroscopic silicon dioxide particles formed by theflame hydrolysis process described above is placed in a beaker of water,the particles are immediately wetted by the water and sink to the bottomof the beaker. However, when another sample of substantially identicalsilicon dioxide particles are treated with dimethyl dichlorosilane sothat approximately percent of the silanol groups on the surface of thesilicon dioxide particles are chemically reacted with the silane, thetreated silicon dioxide particles will float indefinitely on the surfaceof the water in the beaker. When viewed from below, the mass of floatingtreated colloidal silica particles is similar in appearance to floatingmercury because of the substantially total reflection of light. Tofurther illustrate the unusual hydrophobic properties of silicon dioxideparticles such as that described in the beaker of water test, a finemist of water is mixed with a treated silicon dioxide particle andcollected in a beaker. The particles of water are surrounded by thetreated silicon dioxide particles and are prevented from reuniting withother particles of water to form larger particles. In a mixture of about10 percent of treated colloidal silica particles and about percent waterdroplets, the mixture takes on the appearance of a powder. Objectsimmersed in this mixture are not wetted by the water. To furtherillustrate the difference between treated and untreated submicroscopicsilicon dioxide particles, the moisture absorption in terms of mg/ m atdifferent relative humidities are compared. At 40 percent relativehumidity, untreated silicon dioxide particles absorb 4.0 mg/ 100m ofwater and the treated silicon dioxide particles absorb 0.4 m/ 100m ofwater. At 60 percent relative humidity, the untreated silicon dioxideparticles absorb mg/ 100m of water and the treated particles absorb 0.9mg/ 100m of water. At 80 percent humidity, the untreated silicon dioxideparticles absorb 30 mg/lOOm and the treated particles absorb 1.5 mg/100m of water. Thus, at 80 percent relative humidity, the untreatedcolloidal silica particles absorb about times more water than thetreated colloidal silica particles.

Any suitable hydrocarbon or substituted hydrocarbon organic groupdirectly attached to a silicon atom in the organosilicon compound may beemployed. The organic group is preferably hydrophobic to improve thestability of developer materials under varying humidity conditions. Theorganic groups may comprise saturated or unsaturated hydrocarbon groupsor derivatives thereof. Saturated organic groups include methyl, ethyl,propyl, butyl, bromomethyl, chloromethyl, chloroethyl and chloropropylgroups. Typical unsaturated organic groups include: vinyl, chlorovinyl,allyl, allylphenyl, and methacryloxypropyl. The size of the organicgroup attached to a silicon atom in the organosilicon compound dependson numerous factors such as the number of organic groups attached to thesilicon atom, the likelihood of steric hinderance occurring, the numberof silanol groups to be reacted, and the like. The principle criteria isthat at least about 5 percent of the silanol groups on the silicondioxide particles are reacted with the organosilicon compound. Anysuitable hydrolyzable groups may be attached to the silicon atom of theorganosilicon compound. Typical hydrolyzable groups include: chloro,bromo, ethoxy, methoxy, propoxy, propyloxy, acetoxy, and amino groups.Examples of typical organosilicon compounds having an organic groupattached directly to a silicon atom and hydrolyzable groups attached toa silicon atom include: dimethyl dichlorosilane, trimethyl chlorosilane,methyl trichlorosilane, allyl dimethylchlorosilane,hexamethyldisilazane, allylphenyldichlorosilane,benzyldimethylchlorosilane, bromomethyldimethylchlorosilane,alpha-chloroethyltrichlorosilane, betachloroethyltrichlorosilane,chloromethyldimethylchlorosilane, chloromethyltrichlorosilane,p-chlorophenyltrichlorosilane, 3-chloropropyltrichlorosilane,3-chloropropyltrimethoxysilane, vinyltriethoxysilane,vinylmethoxysilane, vinyl-tris (beta-methoxyethoxy) silane,gammamethacryloxypropyltrimethoxysilane, vinyltriacetoxysilane,divinyldichlorosilane, and dimethylvinylchlorosilane. Methylatedchlorosilanes, particularly, dimethyl dichlorosilane, are preferredbecause a greater number of silanol groups per unit area on the silicondioxide particles are reacted with the silanes thereby reducing thehumidity sensitivity of the treated silicon dioxide particles of thisinvention. This high degree of reaction efficiency appears to be due tothe reduced influence of steric hinderance.

Any suitable pigmented or dyed electroscopic toner material may betreated with the additivies of this invention. Typical toner materialsinclude polystyrene resin, acrylic resin, polyethylene resin, polyvinylchloride resin, polyacrylamide resin, methacrylate resin, polyethyleneterephthalate resin, polyamide resin, resinous condensation product of2,2 bis-(4-hydroxyisopropoxy-phenyl) propane and fumaric acid, andcopolymers, polyblends and mixtures thereof. Vinyl resins having amelting point or melting range starting at least about 1 10F. areespecially suitable for use in the toner of this invention. These vinylresins may be a homopolymer or a copolymer of two or more vinylmonomers. Typical monomeric units which may be employed to form vinylpolymers include styrene, vinyl naphthalene, mono-olefins such asethylene, propylene, butylene, isobutylene and the like, vinyl esterssuch as vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrateand the like, esters of alphamethylene aliphatic monocarboxylic acidssuch as methyl acrylate, ethyl acrylate, n-butylacrylate, isobutylacrylate, dodecyl acrylate, n-octyl acrylate, phenyl acrylate methylmethacrylate; ethyl methacrylate, butyl methacrylate and the like: vinylethers such as vinyl methylether, vinyl isobutyl ether, vinyl ethylether, and the like: vinyl ketones such as vinyl methyl ketone, vinylhexyl ketone, methyl isopropenyl ketone and the like: and mixturesthereof. Generally, suitable vinyl resins employed in the toner have aweight average molecular weight between about 3,000 to about 500,000.

Toner resins containing a relatively high percentage of styrene resinare preferred because a greater degree of image definition is achievedwith a given quantity of additive material. Further, denser images areobtained when at least about 25 percent by weight, based on the totalweight of resin in the toner, of a styrene resin is present in thetoner. The styrene resin may be a polymer of styrene or styrenehomologues or copolymers of styrene with other monomeric groupscontaining a single methylene group attached to a carbon atom by adouble bond. Thus, typical monomeric materials which may becopolymerized with styrene by addition polymerization include: vinylnaphthalene; mono-olefins such as ethylene, propylene, butylene,isobutylene and the like: vinyl esters such as vinyl acetate, vinylpropionate, vinyl benzoate, vinyl butyrate and the like; esters ofalpha-methylene aliphatic monocarboxylic acids such as methyl acrylate,ethyl acrylate, n-butylacrylate, isobutyl acrylate, dodecyl acrylate,n-octyl acrylate, phenyl acrylate, methyl methacrylate, ethylmethacrylate, butyl methacrylate and the like; vinyl ethers such asvinyl methyl ether, vinyl isobutyl ether, vinyl ethyl ether, and thelike; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone,methyl isopropenyl ketones and the like; and mixtures thereof. Thestyrene resins may also be formed by the polymerization of mixtures oftwo or more of these unsaturated monomeric materials with a styrenemonomer.

The vinyl resins, including styrene type resins, may also be blendedwith one or more other resins if desired. When the vinyl resin isblended with another resin, the added resin is preferably another vinylresin because the resulting blend is characterized by especially goodtriboelectric stability and uniform resistance against physicaldegradation. The vinyl resins employed for blending with the styrenetype or other vinyl resin may be prepared by the addition polymerizationof any suitable vinyl monomer such as the vinyl monomers describedabove. Other thermoplastic resins may also be blended with the vinylresins of this invention. Typical non-vinyl type thermoplastic resinsinclude: rosin modified phenol formaldehyde resins, oil modified epoxyresins, polyurethane resins, cellulosic resins, polyether resins,polycarbonate resins and mixtures thereof. As indicated above, if theresin component of the toner contains styrene copolymerized with anotherunsaturated monomer or is a blend of polystyrene and other resins, astyrene component of at least about 25 percent, by weight, based on thetotal weight 9 of the resin present in the toner is preferred becausedenser images are obtained and a greater degree of image definition isachieved with a given quantity of additive material.

It is to be understood that the specific description of componentscontained in the additives and resins of this invention represent thevast majority of the components present, but do not exclude the presenceof other monomeric units or reactants than those which have been shown.For example, some commercial materials such as polystyrenes containtrace amounts of homologues or unreacted or partially reacted monomers.Similarly, additive particles containing trace amounts of impuritieshave been described above. Any minor amount of such substituents may bepresent in the materials of this invention.

Any suitable pigment or dye may be employed as the colorant for thetoner particles. Toner colorants are well known and include, forexample, carbon black, Resoform Red BN, Benzidene yellow, nigrosine dye,aniline blue, Calco Oil Blue, chrome yellow, ultramarine blue, duPontOil Red, Quinoli'ne Yellow, methylene blue chloride, phthalocyanineblue, Malachite Green Oxalate, lamp black, Rose Bengal and mixturesthereof. The pigment or dyes should be present in the toner in asufficient quantity to render it highly colored so that it will form aclearly visible image on a recording member. Thus, for example, whereconventional xerographic copies of typed documents are desired, the

toner may comprise a black pigment such as carbon black or a black dyesuch as Amaplast Black Dye, available from the National Aniline ProductsInc. Preferably, the pigment is employed in an amount from about 1percent to about 20'percent, by weight, based on the total weight of thecolored toner. If the toner colorant employed is a dye, substantiallysmaller quantities of colorant may be used. 1 a

The combination of the resin component, colorant and additive, whetherthe resin component is a homopolymer, copolymer or blend, should have ablocking temperature of at least about 1 F. When the toner ischaracterized by a blocking temperature less than about 110F. the tonerparticles tend to agglomerate during storage and machine operation andalso form undesirable films on the surface of reusable photoreceptorswhich adversely affect image quality.

The toner compositions of the present invention may be prepared by anywell known toner mixing and comminution technique. For example,theingredients may be thoroughly mixed by blending, mixing and millingthe components and thereafter micropulverizing the resulting mixture.Another wellknown techniquefor forming toner particles is to spray-dry aball-milled toner composition comprising a colorant, a resin andsolvent. When the toner mixtures of this invention are to be employed ina cascade or magnetic brush development process, the toner should havean average particle size by weight percent less than about 30 microns.For optimum results in cascade development, an average tonerparticle'size between about 4 and about microns is preferred.

Suitable coated and uncoated carrier materials for cascade developmentare well known in the art. The carrier particles comprise any suitablesolid material, provided that the carrier particles acquire a chargehaving an opposite polarity to that of the toner particles when broughtin close contact with the toner particles so that the toner particlescling to and surround the carrier particles. When a positivereproduction of the electrostatic images is desired, the carrierparticle is selected so that the toner particles acquire a charge havinga polarity opposite to that of the electrostatic image. Alternatively,if a reversal reproduction of the electrostatic image is desired, thecarrier is selected so that the toner particles acquire a charge havingthe same polarity as that of the electrostatic image. Thus, thematerials for the carrier particles are selected in accordance with itstriboelectric properties in respect to the electroscopic toner so thatwhen mixed or brought into mutual contact one component of the developeris charged positively if the other component is below the firstcomponent in the triboelectric series and negatively if the othercomponent is above the first component in a triboelectric series. Byproper selection of materials in accordance with their triboelectriceffects the polarities of their charge when mixed are such that theelectroscopic toner particles adhere to and are coated on the surfacesof carrier particles and also adhere to that portion of theelectrostatic image-bearing surface having a greater attraction for thetoner than the carrier particles. Typical carriers, include steel,flintshot, aluminum potassium chloride, Rochelle salt, nickel, aluminumnitrate, potassium chlorate, granular zircon, granular silicon, methylmethacrylate, glass, silicon dioxide and the like. The carriers may beemployed with or without a coating. Many of the foregoing and othertypical carriers are described by L. E. Walkup et al in U.S. Pat. No.2,638,416 and E. N. Wise in U.S. Pat. No. 2,618,552. An ultimate coatedparticle diameter between about 50 microns to about 2,000 microns ispreferred because the carrier particles then possess sufficient densityand inertia to avoid adherence to to electrostatic images .during thecascade development process. Adherence of carrier beads to xerographicdrums is undesirable because of the formation of deep scratches on thesurface during the image transfer and drum cleaning steps. Also printdeletion occurs when large carrier beads adhere to xerographic imagingsurfaces. For magnetic brush development, carrier particles having anaverage particle size less than about 250 microns are satisfactory.Generally speaking, satisfactory results are obtained when about 1 parttoner is used with about 10 to about 1,000 parts by weight of carrier inthe cascade and magnetic brush developers.

The toner compositions of the instant invention may be employed todevelop electrostatic latent images on any suitable electrostatic latentimage-bearing surface including conventional photoconductive surfaces.Well known photoconductive materials include vitreous selenium, organicor inorganic photoconductors embedded in a non-photoconductive matrix,organic or inorganic photoconductors embedded in a photoconductivematrix, or the like. Representative patents in which photoconductivematerials are disclosed include U.S. Pat. No. 2,803,542 to Ullrich, U.S.Pat. No. 2,970,906 to Bixby, U.S. Pat. No. 3,121,006 to Middleton, U.S.Pat. No. 3,121,007 to Middleton, and U.S. Pat. No. 3,151,092 to CorAlthough it is not entirely clear, numerous factors appear to affect theability of the additive particles of this invention to stabilize theperformance of developers in automatic machines. The stabilization ofimages as observed in terms of consistent high quality copies overextended periods of time reduces the need for servicing, extends thedeveloper life, permits the construction of precision close toleranceautomatic machines and eliminates the need to regulate machineenvironment. Factors which may be responsible for the ability of theadditive to improve the stability of developer performance may includethe enormous external surface area, extremely small particle size,relative chemical inertness, low water absorption, high electricalresistivity, high chemical purity, and chemical coupling of theorganosilicon compound to the colloidal silica surface. The externalsurface area of the additive particles of this invention is enormous andranges from below about 50 m /g to above about 400 m /g of externalsurface area (BET). In view of the results achieved, it is hypothesizedthat the enormous external surface area provided by the additiveparticles prevents contaminants from depositing and altering theelectrical characteristics of the carrier, toner and photoreceptorsurfaces. The extremely small size of the additive particles is believedto permit the formation of a barrier layer of additive particles aroundthe toner particles. In support of this belief, it is observed that in asample of toner particles having an average particle size of about 22microns and containing 1 percent by weight based on the weight of thetoner particles of treated additive particles having an average particlesize of about millimicrons, each toner particle is surrounded by about 3million treated silicon dioxide particles. The high electricalresistivity of the treated submicron silicon dioxide particles evenunder exceptionally high humidity conditions appears to reducefluctuations in the electrical properties of the developer under varyingenvironmental conditions. The high chemical purity as well as thechemically bonded organosilicon compound helps reduce the deposition ofcontaminants from the treated additive onto the toner, carrier andphotoreceptor surfaces. The chemical bonding between the organosiliconcompound and the submicroscopic silicon dioxide particles is so strongthat most boiling solvents will not remove the organosilicon compoundfrom the colloidal silica particle surfaces.

Surprinsingly, the developer additive of this invention restoresuntreated developers which have exhibited deterioration in performanceover an extended period of time in automatic electrostatographic imagingmachines. Thus, developers which have deteriorated to the point whereimages have high background toner deposits, reduced resolution, poorimage fill in solid areas, poor image fill in line copies and poor edgedefinition no longer have to be discarded. The mere addition of a smallamount of additive to the deteriorated developer followed by theformation of about 10 to about 30 additional copies with the altereddeveloper mixture restores the imaging performance of the developer tothe level at which it initially performed when freshly introduced intothe machine. The reason for the restorative powers of the additives ofthis invention is not entirely clear. Perhaps the additive particlesremove some of the contaminants which may have deposited on the toner,carrier and photoreceptor. Possible the additive particles alter thedegraded electrical properties of the developer by electricallyinsulating the toner and carrier particles from each other or byaltering the triboelectric properties of the toner and carrierparticles. Although the mechanism through which improvement occurs isnot positively established, the improved results are quite evident. Therelative quantity of additive which may be employed to restore thedeveloper is substantially the same as that which may be employed withfresh developer as described above.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following examples furtherdefine, describe and compare exemplary methods of preparing thedevelopment system components of the present invention and of utilizingthem in a development process. Part and percentages are by weight unlessotherwise indicated. The examples, other than the control examples, arealso intended to illustrate the various preferred embodiments of thepresent invention.

EXAMPLE I The vitreous selenium drum of an automatic copying machine iscorona charged to a positive voltage of about 800 volts and exposed to alight-and-shadow image to form an electrostatic latent image. Theselenium drum is then rotated through a cascade development station. Acontrol developer comprising 1 part toner containing a polystyrene resinprepared by spray drying a solution of polysytrene and about 100 partsof sand core carrier beads prepared by the process disclosed in ExampleII of US. Pat. No. 3,467,634 is employed in the developer station. Thetoner particles have an average particle size of about 12 microns andthe carrier beads have an average particle size of about 600 microns.After the electrostatic latent image is developed in the developingstation, the resulting toner image is transferred to a sheet of paper ata transfer station. The residual toner particles remaining on theselenium drum after passages through the transfer station is removed bymeans of a rotating brush in a vacuum housing. The background density,resolution, image fill in solid areas, image fill in line copies andedge definition are good in the initial copies. However, after 2,000copies are made, background density is very high, resolution hasdecreased, image fill in solid areas is poor, image fill in line copiesis poor and edge definition is poor.

EXAMPLE II The test described in Example I is repeated withsubstantially identical fresh developer mixed with about 0.5 percent byweight treated submicron silicon dioxide particles based on the weightof the toner. The treated silicon dioxide particles are produced byflame hydrolysis decomposition of pure silicon tetrachloride in thegaseous phase in an oxyhydrogen flame at about 1 100C followed byreactions in a heated fluidized bed reactor with dimethyl dichlorosilaneas described in detail above. About percent of the silanol groupspresent on the surface of the freshly prepared silicon dioxide particlesare reacted with the silane in the fluidized bed reactor. The freshlyprepared silicon dioxide particles have about 3 silanol groups per A ofsurface prior to reaction with the silane. Analysis of the treatedsilicon dioxide particles reveals that the particles contain more thanabout 99.8 percent SiO about .9 to about 1.3 percent carbon, about 0.03to about 0.05 percent CI, less than about 0.003 percent heavy metals,less than about 0.003 percent Fe 0 less than about 0.05 percent A1 0less than about 0.03 percent TiO and less than about 0.01 percent Na OThe particle size of the treated silicon dioxide particles is betweenabout 10 to about 30 millimicrons and the surface area of the particlesis about 90 to about 150 m /g. About 10,000 copies are produced with thetreated developer. The image quality of all the copies produced aresuperior in every respect to the copies produced near the termination ofthe test in Example 1.

EXAMPLE III A Xerox 720 automatic copying machine is modified to replacethe cascade development station with a magnetic brush developmentstation. The vitreous selenium drum of the automatic copying machine iscorona charged to a positive voltage of about 800 volts and exposed to alight-and-shadow image to form an electrostatic latent image. Theselenium drumis then rotated through the magnetic brush developmentstation. A control developer comprising one part toner containing about88 percent styrene-butyl methacrylate copolymer and about 3 percentl-amino-4- hydroxyanthraquinone colorant and about 9 percent polyvinylbutyral prepared by conventional blending and micropulverizingtechniques and about 50 parts steel core carrier beads prepared by theprocess disclosed in Example 11 of U.S. Pat. No. 3,467,634 is employedin the development station. The toner particles have an averageparticles size of about 14 microns and the carrier beads have an averageparticle size of about 100 microns. After the electrostatic latent imageis developed in the developing station, the resulting toner image iselectrostatically transferred to a sheet of paper at a transfer station.The residual toner particles remaining on the selenium drum afterpassage through the transfer station is removed by a rotatingcylindrical brush and vacuum system. The test is operated at an averagetemperature of about 75 and a relative humidity of about 32 percent. Thebackground density, resolution, image fill in solid areas, image fill inline copies and edge definition are good in the initial copies. However,after 900 copies are made, background density has more than doubled,resolution has decreased, image fill in solid areas is poor, image fillin line copies is poor and edge definition is poor.

EXAMPLE IV The test described in Example 111 is repeated with freshsubstantially identical developer mixed with about 1 percent ofhydrophobic treated silicon dioxide particles based on the weight of thetoner. The treated silicon dioxide particles have an average particlesize of about 20 millimicrons. An average of at least about 2 siliconatoms per 100A of silicon dioxide particle surface area are chemicallybonded through an oxygen linkage to silicon atoms have two methyl groupsattached thereto. About 10,000 copies are produced with the treateddeveloper. The image quality of all copies produced are superior inevery respect compared to the copies produced near the termination ofthe test described in Example 111.

EXAMPLE V The procedure described in Example 111 is repeated with adeveloper comprising one part toner containing about 95 percentstyrene-butyl methacrylate copolymer and about 5 percent Grasol FastYellow 36L colorant prepared by conventional blending andmicropulverizing techniques and about 100 parts by weight steel beadscoated with a thin ethyl cellulose coating is employed in thedevelopment station. The test is operated at an average temperature ofabout and a relative humidity of about 24 percent. The backgrounddensity, resolution, image fill in solid areas, image fill in line copyareas and edge definition are good in initial copies but extremely poorafter 2,400 copies.

EXAMPLE VI The procedure described in Example V is repeated with freshsubstantially identical developer mixed with about 1.5 percenthydrophobic silicon dioxide particles based on the weight of the toner.This hydrophobic silicon dioxide material is substantially identical tothe treated silicon dioxide particles described in Example 1V. About15,000 copies are produced with the treated developer. The image qualityof all copies produced are superior in every respect compared to thecopies produced near termination of the test described in Example V.

EXAMPLE VII The procedure described in Example II is repeated with adifferent control developer. This new control developer comprises 1 parttoner containing about 97 percent styrene-butyl methacrylate copolymerand about 3 percent purified Resoform Red BN colorant prepared byconventional blending and micropulverizing techniques and about 100parts steel core carrier beads prepared by the process disclosed inExample 11 of US. Pat. No. 3,467,634. The toner particles have anaverage particle size of about 15 microns and the carrier beads have anaverage particle size of about 100 microns. The test is operated at anaverage temperature of about 76 and a relative humidity of about 30percent. The background density, resolution, image fill in solid areas,image fill in line images and edge definition are good in the initialcopies. However, after 4,000 copies are made, resolution has decreased,image fill in solid areas is poor, image fill in line images is poor andedge definition is poor.

EXAMPLE VIII The test described in Example Vll is momentarily stoppedand about 3.5 percent of treated silicon dioxide particles based on theweight of the toner is mixed into the developer. The treated silicondioxide particles have an average particle size between about 10 andabout 30 millimicrons. An average of at least about 3 silicon atoms per100A of the silicon dioxide particle surface area are chemically bondedthrough an oxygen linkage to silicon atoms having two hydrophobicorganic groups attached thereto (Organ-O-Sil S-5, Cabot Corporation).After the treated silicon dioxide particles are added to the developer,250 additional copies are made. The last 225 copies produced aresuperior in every respect compared to the copies produced near thetermination of the test described in Example V1.

EXAMPLE IX A control developer is tested in an automatic copying machineutilizing a web cleaning system. The photoreceptor of the automaticcopying machine is corona charged to a positive voltage of about 700volts and exposed to a light-and-shadow image to form an electrostaticlatent image. The photoreceptor is then rotated through a cascadedevelopment station. The controll developer comprises 1 part tonercomprising about 7 parts styrene-butyl methacrylate copolymer, about 2parts pentaerythritol tetrabenzoate and about 1 part carbon blackcolorant prepared by conventional blending and micropulverizingtechniques and about 125 parts flintshot coated with a thin coating ofethylcellulose. The toner particles have an average particle size ofabout 12 microns and the carrier beads have an average particle size ofabout 700 microns. After the electrostatic latent image is developed inthe developing station, the resulting toner image is electrostaticallytransferred to a sheet 9 of paper at a transfer station. The residualtoner particles remaining on the photoreceptor surface after passagethrough the transfer station is removed by a fibrous web rubbed againstthe photoreceptor surface. The image density is good in the initialcopies with a density reading of about 1.2. However, the image densitydeteriorates to about .8 after about 1,500 copies are made.

EXAMPLE X The procedure described in Example IX is repeated with freshsubstantially identical developer mixed with about 0.5 percent by weighttreated silicon dioxide additive based on the weight of the toner. Theadditive, Aerosil R-972, is substantially identical to the treatedadditive described in Example 11. The initial images formed with thistreated developer are very good with a density of about 1.3. The densityof subsequent images through 4,000 copies remains good. All 4,000 copiesexhibit a density of at least about 1.2.

EXAMPLE Xl A Xerox 720 automatic copying machine with a cascadedevelopment station is employed. The vitreous selenium drum of theautomatic copying machine is corona charged to a positive voltage ofabout 800 volts and exposed to a light-and-shadow image to form anelectrostatic latent image. The selenium drum is then rotated throughthe cascade development station. A control developer comprising one parttoner containing about 90 percent of a resinous condensation product of2,2 bis-(4-hydroxyisopropoxy-phenyl)-propane and fumaric acid and about10 percent carbon black prepared by conventional blending andmicropulverizing techniques, about 1 percent by weight untreated silicondioxide additive based on the weight of the toner and about 100 partsflintshot carrier beads prepared by the process disclosed in Example IIof US. Pat. No. 3,467,634 is employed in the development station. Thetoner particles have an ave rage particle size of about 10 microns andthe carrier beads have an average particle size of about 700 microns.Analysis of the additive, Aerosil 200, reveals that the particlescontain more than 99.8 percent SiO less than about 0.025 percent Hcl,less than about 0.05 percent A1 0 less than about 0.03 percent TiO andless than about 0.003 percent Fe O The particle size of the untreatedsilicon dioxide particles is about 12 millimicrons and the surface areaof the particles is about 175 to about 225 m /g. After the electrostaticlatent image is developed in the developing station, the resulting tonerimage is electrostatically transferred to a sheet of paper at a transferstation. The residual toner particles remaining on the selenium drumafter passage through the transfer station is removed by a rotatingcylindrical brush and vacuum system. The test is operated at an averagetemperature of about degrees and a relative humidity of about percent.The background density, resolution, image fill in line copies and edgedefinition are good in the initial copies. However, after about 900copies are made, background density has more than doubled, resolutionhas decreased, image fill in line copies is poor and edge definition ispoor. The photoreceptor is examined at this point. A dull damp clay-likefilm is observed which cannot be removed by ordinary cleaningtechniques.

EXAMPLE XII The procedure described in Example X1 is repeated with freshsubstantially identical developer mixed with about 1 percent by weighttreated silicon dioxide additive based on the weight of the toner. Thetreated additive Aerosil R-972 is described in detail above in ExampleX. No clay like film is observed on the photoreceptor surface even afterabout 2,500 copies.

Although the treated silicon dioxide particles of the invention aredescribed in terms of individual particles, it is apparent that many ofthe particles agglomerate to fonn larger particles or chains. Theseagglomerates and chains of smaller particles are deemed within the scopeof this invention.

The expression developer material as employed herein is intended toinclude electroscopic toner material or combinations of toner materialand carrier material.

Although specific materials and conditions are set forth in theforegoing examples, these are merely intended as illustrations of thepresent invention. Various other suitable toner components, additives,colorants, carriers and development techniques such as those listedabove may be substituted for those in the examples with similar results.Other materials may also be added to the toner or carrier to sensitize,synergize or otherwise improve the imaging properties or other desirableproperties of the system.

Other modifications of the present invention will occur to those skilledin the art upon a reading of the present disclosure. These are intendedto be included within the scope of this invention.

What is claimed is:

1. An imaging process comprising forming an electrostatic latent imageon an imaging surface and forming a toner image on said imaging surfaceby contacting said imaging surface with an electrostatographicdeveloping mixture comprising particles, said particles including finelydivided toner material having an average particle size less than about30 microns and from about 0.05 percent to 1.5 percent based on theweight of said toner material, of silicon dioxide particles having atleast 0. l5 silicon atoms per A on the surface of said silicon dioxideparticles chemically attached through silicon-oxygen-silicon bonding tosilicon atoms having one to three organic groups directly attachedthereto by silicon-carbon bonding, said silicon dioxide particles havingan average particle size of between about one millimicron and aboutmillimicrons, whereby at least a portion of said finely divided tonermaterial is attracted to and held on said imaging surface in conformanceto said electrostatic latent image.

2. An imaging process comprising forming an electrostatic latent imageon an imaging surface and forming a toner image by contacting saidimaging surface with an electrostatographic developing mixturecomprising particles, said particles including about 1 part bonding tosilicon atoms having one to three hydrophobic organic groups directlyattached thereto by siliconcarbon bonding, said silicon dioxideparticles having an average particle size of between about onemillimicron and about millimicrons, whereby at least a portion of saidfinely divided toner material is attracted to and held on said imagingsurface in conformance to said electrostatic latent image.

52%33 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECION Patent No.3,819,367 Dated June 25. 19m

Inventofls) Arun K, Chatterji; Marianne Custazzo; Demosthemes K,

. Kiriazides It is certified that error appears in theabove-identifiedpatent and that said Letters Patent are hereby correctedas shown below:

Column 1 line 32 kindly delete the word of first occurrence andsubstitute therefor if Column ne 57 kindly delete the word charge andsubstitut therefor "charged",

Column 5, line kindly correct the spelling of flame,

Column 8, line 25 kindly delete the word "polyand b tit t therefor--homopoly- Column 10, line 62 kindly delete the word Cor and substitutetherefor --Corrison,--

Column l3, line S y kindly delete the word *have and substitute thereforthe word "having",

Column 15, line l2 delete the numeral "9,

Column 15, line 57 kindly delete the word "HcL and substitute therefor--HCL--,

Signed and seal-ed this 4th day of February 1975.

(SEAL) Attest: I

MCCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents

2. An imaging process comprising forming an electrostatic latent imageon an imaging surface and forming a toner image by contacting saidimaging surface with an electrostatographic developing mixturecomprising particles, said particles including about 1 part by weight offinely divided toner material having an average particle size less thanabout 30 microns, from about 10 to about 1,000 parts by weight carrierparticles which are grossly larger than said finely divided tonermaterial and from about 0.05 percent to 1.5 percent based on the weightof said toner material of silicon dioxide particles having at least 0.15silicon atoms per A2 on the surface of said silicon dioxide particleschemically attached through silicon-oxygen-silicon bonding to siliconatoms having one to three hydrophobic organic groups directly attachedthereto by silicon-carbon bonding, said silicon dioxide particles havingan average particle size of between about one millimicron and about 100millimicrons, whereby at least a portion of said finely divided tonermaterial is attracted to and held on said imaging surface in conformanceto said electrostatic latent image.